|In most sources the
families in the order Acteonoidea are listed as part of the
Cephalaspidea. However, recent DNA work (Malaquias, et. al., 2009)
supports placing them in their own order. Alternatively, some sources place them within the Acteonimorpha (along with the Rissoellidae). Like the Cephalaspidea, they have a
presumably evolved for burrowing. Unlike the Cephalaspidea, the shell
is always well developed and external. Most are burrowers and
They are carnivores, generally specializing in polychaete worms. At
least three families are found in Hawaii.
The genus Ringicula (family
Ringiculidae) is mentioned only in the
introductory material in Kay, 1979 as part of the molluscan
assemblage found at depths over 200 m. However, it is not
covered in the text nor do we have any other information indicating
that it's been recorded from Hawaii. Some sources place the Ringiculidae outside the Acteonimorpha but in the Euthyneura.
Some authors place these four families in the lower Heterobranchia rather than